Clorofilômetro no ajuste da adubação nitrogenada em cobertura para o milho de alta produtividade

Abstract

The evaluation of the chlorophyll relative content in the leaves provides an indirect measure of the plant's nutritional status and can help farmers to adjust the quantity of nitrogen (N) to be applied as top dressing fertilization for corn. The aim of this work was to validate the use of chlorophyll meter for detection and correction of N deficiency during the crop vegetative growth. The experiment was carried out in plots under commercial crop conditions and the corn nutritional status was monitored weekly with the chlorophyll meter. Six treatments of top dressing N included a check (0kg ha-1) and four doses (45, 90, 135 and 180kg ha-1), considering the nitrogen sufficiency index (NSI) of 0.95 monitored with the chlorophyll meter based on a reference treatment (500kg ha-1). The chlorophyll meter indicated top dress N application for corn up to 180kg ha-1, exceeding the quantities required to maximize the technical (144kg ha-1) or economic (105kg ha-1) efficiency. The establishment of reference plots makes the chlorophyll meter an useful indicator of the need of N top dressing during the corn growth, however, the use of the 0,95 NSI value throughout the crop cycle may not be the most appropriate strategy.